How many people does it take to take up all the space in the ocean?

This question is so weird that I find it intriguing, but mostly on the level of "who came up with this, and why?" I can't actually answer the question because so far as I know, the volume of water in the Earth's oceans is unknown. We do know that oceans cover about 75% of the Earth's surface. Something in the neighborhood of 6 billion people occupy the remaining 25% without accidentally poking one another in the eye all the time. This crude math tells me that it would take a minimum of 24 billion people to (comfortably) cover the surface of the Earth, 18 billion of them on the ocean. But the ocean is also extremely deep. The Marianas Trench, located in the Pacific Ocean, could theoretically submerge Mount Everest with 2 kilometers of water to spare. How many people is that?